1. Field of the Invention
The present invention relates to a dielectric filter, a dielectric duplexer, a mounting structure having the same, and a communication device.
2. Description of the Related Art
In recent years, radio wave communication equipment, such as portable telephones and the like, of small in size, light in weight, and thin types have been spread widely and rapidly. With the spread, it has been more intensively needed to develop dielectric filters and dielectric duplexers, to be mounted on the equipment of the above-mentioned type, which are small in size, light in weight, and low in height.
Conventionally, a dielectric filter of the above-mentioned type, shown in FIG. 11, has been known. A dielectric filter 8 comprises a plurality of resonator holes 3 provided in a single dielectric block 2 which has an outer conductor 1 provided on the surface thereof. An inner conductor 4 is provided on the inner surface of each resonator hole 3. The inner conductor 4 is electrically connected to the outer conductor 1, at the side surface 2b of the dielectric block 2, shown as the back-face of the dielectric filter 8 in FIG. 11, and is electrically left unconnected to the outer conductor 1 at the side surface 2a shown as the front-face in FIG. 11.
Ordinarily, the dielectric filter 8 is so mounted onto a circuit board 6 that the axes of the resonator holes 3 are in parallel to the circuit board 6. To reduce the height of the dielectric filter 8 having the above-described mounting form, the method may be supposed by which the diameters of the resonator holes 3 are decreased in order that the height h of the dielectric block 2 is reduced. However, it is difficult to form the dielectric block 2 by means of a metallic mould, due to the resonator holes 3 having a reduced diameter. In general, the dielectric filter 8 has a high Q.sub.0. To obtain the high Q.sub.0, it is necessary to assure the optimum height h with respect to the diameter of each resonator hole 3. For this reason, it is problematic to reduce the height of the dielectric filter 8. In some cases, an electromagnetic field leaking from the side surface 2a, which is an open-circuited surface, exerts a hazardous influence over the characteristics of other electronic components mounted onto a circuit board 6. Similarly, in some cases, an electromagnetic field leaking from the other electronic components unfavorably affects the characteristics of the dielectric filter 8.